Psttm device with multi-layered filter stack

ABSTRACT

MTJ material stacks, pSTTM devices employing such stacks, and computing platforms employing such pSTTM devices. In some embodiments, perpendicular MTJ material stacks include a multi-layered filter stack disposed between a fixed magnetic layer and an antiferromagnetic layer or synthetic antiferromagnetic (SAF) stack. In some embodiments, non-magnetic layers of the filter stack include at least one of Ta, Mo, Nb, W, or Hf. These transition metals may be in pure form or alloyed with other constituents.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application contains subject matter related to PCT ApplicationPCT/US15/52292 (Docket No. 01.P87084PCT), titled “PSTTM DEVICE WITH FREEMAGNETIC LAYERS COUPLED THROUGH A METAL LAYER HAVING HIGH TEMPERATURESTABILITY” filed on Sep. 25, 2015, and PCT Application US15/______(Docket No. 01.P87086PCT), titled “PSTTM DEVICE WITH BOTTOM ELECTRODEINTERFACE MATERIAL” filed on Sep. 25, 2015.

BACKGROUND

STTM devices are non-volatile memory devices that utilize a phenomenonknown as tunneling magnetoresistance (TMR). For a structure includingtwo ferromagnetic layers separated by a thin insulating tunnel layer, itis more likely that electrons will tunnel through the tunnel layer whenmagnetizations of the two magnetic layers are in a parallel orientationthan if they are not (non-parallel or antiparallel orientation). Assuch, a magnetic tunneling junction (MTJ), typically comprising a fixedmagnetic layer and a free magnetic layer separated by a tunnelingbarrier layer, can be switched between two states of electricalresistance, one state having a low resistance and one state with a highresistance. The greater the differential in resistance, the higher theTMR ratio: (R_(AP)-R_(p)/R_(p)*100% where R_(p) and R_(AP) areresistances for parallel and antiparallel alignment of themagnetizations, respectively. The higher the TMR ratio, the more readilya bit can be reliably stored in association with the MTJ resistivestate. The TMR ratio of a given MTJ is therefore an importantperformance metric of an STTM.

For an STTM device, current-induced magnetization switching may be usedto set the bit states. Polarization states of one ferromagnetic layercan be switched relative to a fixed polarization of the secondferromagnetic layer via the spin transfer torque phenomenon, enablingstates of the MTJ to be set by application of current. Angular momentum(spin) of the electrons may be polarized through one or more structuresand techniques (e.g., direct current, spin-hall effect, etc.). Thesespin-polarized electrons can transfer their spin angular momentum to themagnetization of the free layer and cause it to precess. As such, themagnetization of the free magnetic layer can be switched by a pulse ofcurrent (e.g., in about 1-10 nanoseconds) exceeding a certain criticalvalue, while magnetization of the fixed magnetic layer remains unchangedas long as the current pulse is below some higher threshold associatedwith the fixed layer architecture.

For a pSTTM device, MTJs include magnetic electrodes having aperpendicular (out of plane of substrate) magnetic easy axis and canrealize higher density memory than in-plane variants. Perpendicularmagnetic anisotropy (PMA) can be achieved in the fixed magnetic layerthrough interfacial perpendicular anisotropy promoted by an adjacentlayer during solid phase epitaxy.

An anti-ferromagnetic layer or a synthetic antiferromagnetic (SAF)structure within an MTJ stack can improve device performance bycountering a fringing magnetic field associated with the fixed magneticmaterial layer. A filter or barrier material layer is typically insertedbetween the fixed magnetic material layer and SAF structure to decouplethe crystallinity of materials employed in the SAF from that of thefixed magnetic material layer. Without a filter layer it is difficult toachieve perpendicular anisotropy in the fixed layer at high annealtemperatures. The higher TMR achieved with a filtered SAF structure hasnot proven robust to high temperature processing (e.g., 400° C.), withTMR often degrading to 100%, or less, as thermal treatments exceed 300°C. This loss of TMR renders such a MTJ material stack difficult tointegrate with MOS transistor IC fabrication. A filter capable ofimproving the stability of the fixed layer that can sustain hightemperature processing is therefore advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

The material described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements. In thefigures:

FIG. 1 is a cross-sectional view of a material layer stack for a pSTTMdevice including a multi-layered filter stack, in accordance with someembodiments of the present invention;

FIG. 2 is a graph of material layer stack sheet resistance as a functionof applied magnetic field strength, in accordance with some embodiments;

FIG. 3 is a graph comparing TMR % for material layer stacks including amulti-layer filter stack with different non-magnetic material layers, inaccordance with some embodiments;

FIG. 4 is a cross-sectional view of a material layer stack for a pSTTMdevice further including a multi-layered magnetic material stack, inaccordance with some further embodiments of the present invention;

FIG. 5 is a cross-sectional view of a material layer stack for a pSTTMdevice further including an electrode interface material, in accordancewith some further embodiments of the present invention;

FIG. 6 is a flow diagram illustrating a method of fabricating the pSTTMdevice illustrated in FIG. 1, in accordance with some embodiments;

FIG. 7 is a schematic of a STTM bit cell, which includes a spin transfertorque element, in accordance with an embodiment of the presentinvention;

FIG. 8 is a schematic illustrating a mobile computing platform and adata server machine employing STTM arrays, in accordance withembodiments of the present invention; and

FIG. 9 is a functional block diagram illustrating an electroniccomputing device, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

One or more embodiments are described with reference to the enclosedfigures. While specific configurations and arrangements are depicted anddiscussed in detail, it should be understood that this is done forillustrative purposes only. Persons skilled in the relevant art willrecognize that other configurations and arrangements are possiblewithout departing from the spirit and scope of the description. It willbe apparent to those skilled in the relevant art that techniques and/orarrangements described herein may be employed in a variety of othersystems and applications other than what is described in detail herein.

Reference is made in the following detailed description to theaccompanying drawings, which form a part hereof and illustrate exemplaryembodiments. Further, it is to be understood that other embodiments maybe utilized and structural and/or logical changes may be made withoutdeparting from the scope of claimed subject matter. It should also benoted that directions and references, for example, up, down, top,bottom, and so on, may be used merely to facilitate the description offeatures in the drawings. Therefore, the following detailed descriptionis not to be taken in a limiting sense and the scope of claimed subjectmatter is defined solely by the appended claims and their equivalents.

In the following description, numerous details are set forth. However,it will be apparent to one skilled in the art, that the presentinvention may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present invention.Reference throughout this specification to “an embodiment” or “oneembodiment” means that a particular feature, structure, function, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” or “in one embodiment” in various placesthroughout this specification are not necessarily referring to the sameembodiment of the invention. Furthermore, the particular features,structures, functions, or characteristics may be combined in anysuitable manner in one or more embodiments. For example, a firstembodiment may be combined with a second embodiment anywhere theparticular features, structures, functions, or characteristicsassociated with the two embodiments are not mutually exclusive.

As used in the description of the invention and the appended claims, thesingular forms “a”, “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willalso be understood that the term “and/or” as used herein refers to andencompasses any and all possible combinations of one or more of theassociated listed items.

The terms “coupled” and “connected,” along with their derivatives, maybe used herein to describe functional or structural relationshipsbetween components. It should be understood that these terms are notintended as synonyms for each other. Rather, in particular embodiments,“connected” may be used to indicate that two or more elements are indirect physical, optical, or electrical contact with each other.“Coupled” may be used to indicated that two or more elements are ineither direct or indirect (with other intervening elements between them)physical or electrical contact with each other, and/or that the two ormore elements co-operate or interact with each other (e.g., as in acause an effect relationship).

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one component or material with respect to othercomponents or materials where such physical relationships arenoteworthy. For example in the context of materials, one material ormaterial disposed over or under another may be directly in contact ormay have one or more intervening materials. Moreover, one materialdisposed between two materials or materials may be directly in contactwith the two layers or may have one or more intervening layers. Incontrast, a first material or material “on” a second material ormaterial is in direct contact with that second material/material.Similar distinctions are to be made in the context of componentassemblies.

As used throughout this description, and in the claims, a list of itemsjoined by the term “at least one of” or “one or more of” can mean anycombination of the listed terms. For example, the phrase “at least oneof A, B or C” can mean A; B; C; A and B; A and C; B and C; or A, B andC.

Described herein are MTJ material stacks, STTM devices employing suchmaterial stacks, and computing platforms employing such STTM devices. Insome embodiments, perpendicular MTJ material stacks include fixedmagnetic layers magnetically coupled to a multi-layer filter stack forimproved temperature stability. Applications for embodiments describedherein include embedded memory, embedded non-volatile memory (NVM),magnetic random access memory (MRAM), and non-embedded or stand-alonememories.

FIG. 1 is a cross-sectional view of a MTJ material stack 101 for a pSTTMdevice, in accordance with some embodiments of the present invention.MTJ material stack 101 includes a first metal electrode 107 (e.g.,bottom electrode) disposed over a substrate 105. MTJ material stack 101further includes a SAF stack 112 disposed over metal electrode 107.Although not depicted, one or more material layers may be disposedbetween SAF stack 112 and metal electrode 107 and/or metal electrode 107may comprise a plurality of material layers. In some exemplaryembodiments, SAF stack 112 includes a first plurality of bilayers 113forming a superlattice of ferromagnetic material (e.g., Co, CoFe, Ni)and a nonmagnetic material (e.g., Pd, Pt, Ru). Bi-layers 113 may includen bi-layers (e.g., n [Co/Pt] bilayers, or n [CoFe/Pd] bilayers, etc.)that are separated from a second plurality of bilayers 115 (e.g., p[Co/Pt]) by an intervening non-magnetic spacer 114. Layer thicknesseswithin bi-layers 113 and 115 may range from 0.1-0.4 nm, for example.Spacer 114 provides the antiferromagnetic coupling between 113 and 115.Spacer 114 may be a Ruthenium (Ru) layer less than 1 nm thick, forexample.

A fixed magnetic material layer or stack 120 including one or more layerof magnetic material is disposed over SAF stack 112. A tunnelingdielectric material layer 130 (e.g., MgO, MgAlO) is disposed over fixedmagnetic material layer or stack 120. A free magnetic material layer orstack 140 is disposed over tunneling dielectric material layer 130. Freemagnetic material layer or stack 140 includes one or more free magneticmaterial layers. In the exemplary embodiment, a dielectric materiallayer 170, such as a metal oxide (e.g., MgO, VdO, TaO, HfO, WO, MoO), isdisposed over free magnetic material layer/stack 140. Such a cappinglayer may be absent for spin-hall effect (SHE) implementations. A secondmetal electrode 180 (e.g., top electrode) is disposed over the cappingmaterial layer 170. Notably, the order of the material layers 107-180may be inverted, or extending laterally away from a topographic featuresidewall, in alternative embodiments.

In some embodiments, the material stack shown in FIG. 1 is aperpendicular system, where spins of the magnetic layers areperpendicular to the plane of the material layers (i.e., the magneticeasy axis is in the z-direction out of the plane of substrate 105).Fixed magnetic layer 120 may be composed of any material or stack ofmaterials suitable for maintaining a fixed magnetization direction whilethe free magnetic material stack 155 is magnetically softer (i.e.magnetization can easily rotate to parallel and antiparallel state withrespect to fixed layer). In some embodiments, MTJ structure 101 is basedon a CoFeB/MgO system, having an MgO tunneling material layer 130, CoFeBfixed magnetic layer/stack 120, and CoFeB free magnetic layer(s) 140. Inadvantageous embodiments, all CoFeB layers have (001) out-of-planebody-centered cubic (BCC) texture, where texture refers to thedistribution of crystallographic orientations within in the layers ofMTJ structure 101. For at least some such embodiments, a high percentageof crystals of the CoFeB/MgO/CoFeB structure 103 have the preferred(001) out-of-plane orientation (i.e., the degree of texture is high). Insome CoFeB/MgO embodiments, the (001) oriented CoFeB magnetic materiallayers 120, and 140 are iron-rich alloys (i.e., Fe>Co) for increasedmagnetic perpendicularity. In some embodiments, Fe content is at least50%. Exemplary embodiments include 20-30% B (e.g., Co₂₀Fe₆₀B₂₀). Otherembodiments with equal parts cobalt and iron are also possible (e.g.,Co₄₀Fe₄₀B₂₀). Other magnetic material compositions are also possible forthe fixed and/or free magnetic layers, such as but not limited to: Co,Fe, Ni, and non-boron alloys of these metals (e.g., CoFe). Filmthickness of fixed and free magnetic layers 120, 140 may be 0.1-2.0 nm.

Tunneling dielectric material layer 130 is composed of a material orstack of materials suitable for allowing current of a majority spin topass through the layer, while impeding current of a minority spin (i.e.,a spin filter), impacting the tunneling magneto-resistance associatedwith MTJ material stack 101. In some exemplary embodiments, dielectricmaterial layer 130 is magnesium oxide (MgO). Dielectric material layer130 may further provide a crystallization template (e.g.,polycrystalline BCC with (001) texture) for solid phase epitaxy of freemagnetic material layer(s) 140 and/or fixed magnetic material layer(s)120, particularly for CoFeB/MgO/CoFeB embodiments.

Fixed magnetic material layer(s) 120 is magnetically coupled to SAFstack 112 through multi-layered filter stack 116 having high temperature(HT) tolerance. As employed herein, high temperature tolerance of thefilter stack is in reference to the ability of the filter to maintaindesirable fixed magnetic layer characteristics impacting temperaturestability and TMR of MTJ material stack 102 through subsequent thermaltreatments associated with integrated circuit device fabrication (e.g.,400° C.).

In exemplary embodiments, filter stack 116 includes at least oneferromagnetic (FM) material layer 118 disposed between a firstnon-magnetic (NM) material layer 117 and second NM material layer 119.FM material layer 118 may be of any ferromagnetic composition, such asbut not limit to Co, Fe, Ni, and alloys of these metals. In someadvantageous embodiments, FM material layer 118 is CoFeB. The CoFeBcomposition may be the same as that of fixed magnetic material layer(s)120, and/or the same as that of free magnetic material layer(s) 140. Insome CoFeB embodiments where both fixed magnetic layer(s) 120 and freemagnetic(s) 140 are Fe-rich (Fe>Co), FM material layer 118 is alsoFe-rich CoFeB, and may be 50-60% Fe. In some Fe-rich CoFeB embodiments,each of magnetic material layers 118, 120, 140 is CoFeB with 20-30% B(e.g., Co₂₀Fe₆₀B₂₀).

In accordance with some embodiments of multi-layered filter stack 116,at least one of NM material layers 117, 119 comprises a transition metalselected from the group consisting of Ta, Mo, Nb, W, and Hf. Thetransition metal may be in pure form or alloyed with other constituents.In advantageous embodiments, at least one NM material layer in filterstack 116 is predominantly (i.e., the constituent of greatest proportionin the NM material layer) one of Ta, Mo, Nb, and Hf In some advantageousembodiments, at least one NM material layer in filter stack 116 is Ta(i.e., an NM material layer consists only of Ta).

In accordance with further embodiments, both NM material layers 117, 119comprises a transition metal selected from the group consisting of Ta,Mo, Nb, and Hf. In accordance with some such embodiments, both NMmaterial layers 117, 119 comprise the same transition metal selectedfrom the group consisting of Ta, Mo, Nb, and Hf. For example, in someembodiments both NM material layers 117 and 119 consist of Ta, orcomprise Ta in a Ta alloy of the same composition). In accordance withalternative embodiments, NM material layers 117, 119 comprise adifferent transition metal selected from the group consisting of Ta, Mo,Nb, and Hf, or comprise different alloys thereof. For example, in someembodiments a first of NM material layers 117 and 119 consists of Ta, orcomprises Ta in a first Ta alloy, while a second of NM material layers117 and 119 consists of Mo, Nb, Hf, comprises Ta in a second Ta alloy,or comprises an alloy of Mo, Nb, or Hf.

In accordance with other embodiments, only one of NM material layers117, 119 comprises a transition metal selected from the group consistingof Ta, Mo, Nb, and Hf, while the other NM material layer is an alternatemetal, such as, but not limited to W, and alloys thereof.

The thickness of the NM material layers in filter stack 116 has alsobeen found to be important with greater thicknesses permissible formaterials providing stronger magnetic coupling. In some embodiments, FMmaterial layer 118 has a thickness less than lnm, and for CoFeBembodiments is advantageously 0.4-0.9 nm. In some exemplary Fe-rich 20%Bembodiments (e.g., Co₂₀Fe₆₀B₂₀), FM material layer 118 has a thicknessbetween 0.7 and 0.9 nm. NM material layers 117, 119 may also havethicknesses less than 1 nm, and advantageously 0.1 nm-0.5 nm. In someembodiments, thicknesses of NM material layers 117 and 119 are notequal. For example, thickness of NM material layer 119 may be thickerthan NM material layer 117 by at least 0.1 nm, with each having athickness of 0.2-0.5 nm.

The inventors have investigated exemplary CoFeB/MgO/CoFeB MTJ stacks andhave found evidence indicating that the set of transition metalsprovided above may offer a significant improvement in at leasttemperature stability of the MTJ device relative to alternative metal,such as W. FIG. 2 is a graph of an MTJ material layer stack sheetresistance as a function of applied magnetic field strength, inaccordance with some embodiments. The illustrated measurements werecollected from samples having a full MTJ stack, such as that illustratedin FIG. 1. In one MTJ stack treatment, the multi-layered filter includesNM material layers consisting of W. In the other MTJ stack treatment,the multi-layered filter includes NM material layers consisting of Ta.The filter layer thicknesses are the same and all other material layersand thickness are substantially the same between the two treatments.Prior to measurement, the material stacks were annealed at a temperatureof 400° C. for 30 mins to simulate subsequent HT processing. In FIG. 2,stacked arrows 201, 202, and 203 illustrate directions of magnetizationin fixed and free magnetic materials associated with the visible changesin the sheet resistance (R_(sq)). In the case that the spin direction isup (majority) in the free magnetic layer(s), a low resistive stateexists, and the directions of magnetization in the free magneticlayer(s) and the fixed magnetic layer(s) are parallel with one another.In the case that the spin direction is down (minority) in the freemagnetic layer(s), a high resistive state exists and the directions ofmagnetization in the free magnetic layer(s) and the fixed magneticlayer(s) are anti-parallel with one another.

As shown in FIG. 2 for the MTJ stack including a W-based filter stack, astrong applied field in a first direction (e.g., −1000 Oe) induces a lowresistance state associated with both fixed and free magnetic materialsbeing magnetically oriented in a first parallel direction as representedby arrows 201. As the applied field changes direction, resistanceincreases to a high resistance state associated with antiparallel fixedand free magnetic orientation represented by arrows 202. The switch toanti-parallel state in the presence of the applied field illustrates thesofter magnetism of the free magnetic layer. As the field furtherincreases in strength, material stack resistance decreases back to thelow resistance value when both fixed and free magnetic layers becomeoriented in a second parallel direction represented by arrows 203. Thefield strength required to switch the fixed layer in this manner isindicative of the fixed magnetic layer stability. As further shown inFIG. 2 the fixed layer in the MTJ stack including a Ta-based filterstack (e.g., both NM material layers being Ta) does not switch in thepresence of the stronger applied magnetic field. In other words,constant R_(sq) value over a wider applied field range 205 indicates thefixed magnetic layer for an MTJ with the Ta-based multi-layered filteris more stable than is the fixed magnetic layer for an MTJ with theW-based multi-layered filter.

FIG. 3 is a graph comparing TMR % for MTJ material layer stacksincluding a multi-layer filter stack with different non-magneticmaterial layers, in accordance with some embodiments. The illustratedmeasurements were collected from samples having a full MTJ stack, suchas that illustrated in FIG. 1. In one MTJ stack treatment, themulti-layered filter stack includes two NM material layers consisting ofW with a CoFeB material layer disposed between the W layers. In theother MTJ stack treatment, the multi-layered filter includes two NMmaterial layers consisting of Ta with a CoFeB material layer disposedbetween the Ta layers. The filter layer thicknesses are the same and allother material layers and thickness are substantially the same betweenthe two treatments. As shown, both multi-layered filters provide a TMRof approximately 200%. As such, the Ta-based multi-layered filterprovides an improvement in fixed layer stability without any TMR penaltyrelative to a W-based multi-layered filter.

A good NM material for a multi-layered filter is one that promotesdesirable crystallinity within the magnetic layers, and therefore is atleast amorphous in the as-deposited state and advantageously has adominant stable phase with BCC crystallinity and (001) texture for CoFeBembodiments of the FM material. All of the transition metals listedabove have BCC stable phases, but so too does W, and thereforeadditional factors may be driving the improved fixed magnetic layerstability illustrated in FIG. 2. Film composition and the attendantcrystallographic and interface properties may impact, for example,magnetic coupling strength of the NM material, as well as solid phaseepitaxy of the free magnetic layers. Interactions of these parametersintroduce complexity in architecting a filter material stack havingtolerance to high temperature processing. The NM material layers (andtechnique for depositing the NM material layers) may also have asignificant role in the formation of magnetic dead zones during hightemperature processing, particularly within a magnetic materialunderlayer upon which a NM material layer is deposited. Although notbound by theory, one possible explanation for the improved stability ofTa relative W illustrated in FIG. 2 is a reduction in magnetic deadzones in the (CoFeB) FM material layer 118, and/or a reduction inmagnetic dead zones in the (Co/Pt) bi-layers 115. Such dead zonereductions would increase the effective thickness of the magneticmaterial layers. A reduction in the magnetic dead zone may beattributable to a lower atomic mixing of the underlying magneticmaterial. Ta has a slightly lower atomic number (Z) than W, for example,and may be deposited with lower energy. Even lighter metals, such as Mo,may advantageously reduce dead zone thickness even more relative to theW reference. Sputter deposition conditions may also vary as a functionof source target material leading to a lower energy deposition of Ta.The NM material layers may also getter dopants from the magnetic layers(e.g., getter B from CoFeB) to different extent, which is currentlythought to improve the crystallization of the magnetic layers. Greatereffective thicknesses and/or improved crystallization of the FM materiallayer would improve coupling strengths between SAF stack 112 and fixedmagnetic material layer 120, increasing stability. Low rates ofdiffusion of the NM material into the FM material may also be importantfor a multi-layered filter stack. Elements of higher Z tend to diffuseless rapidly, so depending also on the magnetic material, the lightesttransition metals provided above (e.g., Mo) may not be as suitable as Taeven though less mixing may occur.

In further reference to FIG. 1, it is noted an MTJ stack may varyconsiderably above tunneling layer 130 and below SAF stack 112 withoutdeviating from the scope of the embodiments of the present invention.For example, a free magnetic material stack including a plurality offree magnetic layers may be incorporated with the filter material stackarchitectures described above. In another example, an electrodeinterface layer may be incorporated between a SAF structure and anunderlying electrode metal to further improve stability of the fixedmagnetic material layer(s).

FIG. 4 is a cross-sectional view of a material layer stack 501 for apSTTM device further including a multi-layered free magnetic materialstack 455, in accordance with some further embodiments of the presentinvention. Free magnetic material stack 455 includes a plurality of freemagnetic material layers magnetically coupled through an interveningmetal coupling material layer. In the exemplary embodiment a metalcoupling material layer 150 is disposed between a first free magneticmaterial layer 140 and a second free magnetic material layer 160.

In some embodiments, layers of a free magnetic material stack 455 aremagnetically coupled through a metal coupling layer 160 having hightemperature (HT) tolerance. As employed herein, high temperaturetolerance of the metal coupling layer is in reference to the ability ofthe coupling material to maintain desirable free magnetic layercharacteristics, (e.g., high stability

and high anisotropy k_(eff)) through subsequent thermal treatmentsassociated with integrated circuit device fabrication. Notably, a vacuumthermal anneal (e.g., ˜250-300° C.) is typically performed to allowmagnetic materials reach a desirable crystallinity and texture (e.g.,BCC with (001) texture) from substantially amorphous as-deposited state.However, many processes conventional to MOS transistor integratedcircuitry (IC) fabrication are performed at 400° C. The inventors havefound that many free magnetic material stacks incorporating a couplingmaterial layer suffer significant degradation in K_(eff) as thermaltreatments exceed 300° C., rendering such a MTJ material stack difficultto integrate with MOS transistor IC fabrication.

In some advantageous embodiments, layers of free magnetic material stack455 are magnetically coupled through a coupling layer 150 comprising atleast molybdenum (Mo). The Mo may be in pure form or alloyed with otherconstituents. In advantageous embodiments, the metal coupling materiallayer is at least predominantly Mo (e.g., Mo is the constituent ofgreatest proportion in the coupling material). In some exemplaryembodiments, the coupling material is elemental Mo (i.e., no otherintentional constituents). In alloyed Mo embodiments, the alloyconstituents may be substantially absent from the free magneticmaterials, or may also be present in the free magnetic materials. Inadvantageous alloyed Mo embodiments, the Mo alloy has a dominant stableBCC phase. In some exemplary embodiments Mo is alloyed one or more ofTa, W, Nb, V, Hf and Cr. The thickness of the coupling material layerhas also been found to be important, advantageously being just a fewangstroms to minimize damping. In some embodiments of a Mo couplinglayer, the Mo film has a thickness less than lnm, and advantageously 0.1and 0.8 nm.

In some embodiments, free magnetic layers 140 and 160 are both CoFeBwith have body-centered cubic (BCC) (001) out-of-plane texture. For atleast some CoFeB embodiments, a high percentage of CoFeB crystals havethe preferred (001) out-of-plane orientation (i.e., the degree oftexture is high). In some embodiments, the (001) oriented CoFeB magneticmaterial layers 120, 140, and 160 are iron-rich alloys (i.e., Fe>Co) forincreased magnetic perpendicularity. Other magnetic materialcompositions are also possible for the fixed and/or free magneticlayers, such as but not limited to: Co, Fe, Ni, and non-boron alloys ofthese metals (e.g., CoFe). In some advantageous embodiments, filmthickness of free magnetic layer 140 is 0.6-1.6 nm, while film thicknessof free magnetic layer 160 is 0.1-1 nm. Free magnetic layer 140 may bethicker than free magnetic layer 160 to compensate any remaining deadregion. In some embodiments however, free magnetic layers 140 and 160have equal thickness as Mo coupling layers have been found to improveperformance in a manner that suggest reduced dead layer thicknesses.

FIG. 5 is a cross-sectional view of a material layer stack 502 for apSTTM device further including an electrode interface materiallayer/stack 110, in accordance with some further embodiments of thepresent invention. In the exemplary embodiment illustrated, electrodeinterface material layer or stack 110 is disposed between electrode 107and SAF stack 112. A seed layer 111 is further disposed between SAFstack 112 and interface material layer/stack 110. Seed layer 111 may beof a material having suitable composition and microstructure to promoteadvantageous crystallinity in SAF stack 112. In some embodiments, seedlayer 111 comprises Pt and may be a substantially pure Pt (i.e. notintentionally alloyed). A seed layer of Pt is well-suited as anunderlayer of a Co/Pt-based SAF structure. Electrode interface materiallayer or stack 110 is to promote an advantageous FCC structure with(111) texture in the seed layer. A Pt seed layer often deposits with FCCstructure unless strongly templated by an underlayer. The presence ofelectrode interface material layer/stack 110 is to prevent seed layerfrom templating its crystal structure based on electrode 107, such as asurface of TiN. As such, electrode interface material layer/stack 110may then be considered a crystal enhancing layer, enhancing thecrystallinity of seed layer 111 (and SAF stack 505, etc.) relative tothe crystallinity achieved when a seed layer is deposited directly onelectrode 107.

In accordance with some embodiments, electrode interface material/stack110 includes at least one material layer comprising CoFeB. For example,a single CoFeB material layer may be in direct contact with both metalelectrode 107 and seed layer 111. For CoFeB electrode interfaceembodiments, seed layer 111 should be sufficiently thick to avoidmagnetic coupling to electrode interface material/stack 110. Forexemplary Pt seed layer embodiments, the Pt layer advantageously has athickness of at least 2 nm (e.g., 2-5 nm).

A CoFeB material layer 110 may have a wide range of compositions asmagnetic properties need not be optimized in the manner typical for freeand/or fixed magnetic layers. In some advantageous embodiments, CoFeBmaterial layer 110A has the same composition as that of fixed magneticmaterial layer(s) 120, and/or the same as that of free magnetic materiallayer(s) 140. CoFeB material layer 110A may have a thickness between 0.4and 5 nm.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a CoFeB material layer in direct contactwith seed layer 111 and a Ta material layer in direct contact with metalelectrode 107. The addition of Ta material layer may improve adhesion ofCoFeB material layer to metal electrode 107 (e.g., a TiN material). TheTa material layer may have a thickness of 5 nm or less (e.g., 1-5 nm),for example.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a Ta material layer in direct contact withseed layer 111, and a Ru material layer in direct contact with metalelectrode 107. The inventors have found Ru deposited with HCPcrystallinity promotes BCC crystallinity in a Ta material layer, whichhas further been found to favor formation of FCC crystallinity and (111)texture within the seed layer. The Ru material layer may have athickness of 20 nm or less, and advantageously 10-20 nm.

In accordance with some further embodiments, electrode interfacematerial/stack 110 includes a Ta material layer in direct contact withseed layer 111 and in direct contact with metal electrode 107. Theinventors have found an elemental (pure) Ta can be employed withoutCoFeB or Ru if the Ta material layer is limited to less than 2 nm, andadvantageously 1.0-1.5 nm. The inventors have found crystallinity for Talimited to less than 1.5 nm in thickness favors formation of FCCcrystallinity and (111) texture within the seed layer.

MTJ material stacks in accordance with the architectures above may befabricated by a variety of methods applying a variety of techniques andprocessing chamber configurations. FIG. 6 is a flow diagram illustratinga method 601 for fabricating the STTM device illustrated in FIG. 1, inaccordance with some embodiments. Method 601 begins with receiving asubstrate at operation 610. Any substrate known to be suitable formicroelectronic fabrication may be received, such as, but not limited tocrystalline silicon substrates. Transistors and/or one or more levels ofinterconnect metallization may be present on the substrate as receivedat operation 610.

At operation 615, a first electrode metal later or stack is deposited.At operation 620, a SAF structure (or antiferromagnetic material layer)is deposited over the first electrode metal layer. At operation 625, afirst Ta layer is deposited directly on a layer of the SAF structure (orantiferromagnetic material layer). At operation 630, a CoFeB layer isdeposited directly on the Ta layer deposited at operation 625. Atoperation 635, a second Ta layer is deposited directly on the CoFeBlayer deposited at operation 630. In alternative embodiments, an alloyof Ta is deposited at operations 625 and 635. In still otherembodiments, at least one of Mo, Nb, or Hf, or alloys thereof isdeposited at least one of operations 625 and 635. For embodiments whereTa, Mo, Nb, or Hf, or alloy thereof is deposited at only one ofoperations 625 and 635, another metal, such as W, may be deposited atthe other operation.

Each of the filter layer materials deposited at operations 625, 630, and635 may be deposited to within the thickness ranges described elsewhereherein. In exemplary embodiments, operations 625, 630, and 635 allentail a physical vapor deposition (sputter deposition) performed at atemperature below 250° C. One or more of co-sputtering and reactivesputtering may be utilized in any capacity known in the art to form thevarious layer compositions described herein. For PVD embodiments, one ormore of the material layers, such as but not limited to the magneticfilter material layer, is deposited in amorphous form that may bediscontinuous over a substrate area (e.g., forming islands that do notcoalesce). Alternate deposition techniques, such as atomic layerdeposition (ALD) may be performed for those materials having precursorsknown to be suitable. Alternatively, epitaxial processes such as, butnot limited to, molecular beam epitaxy (MBE) may be practiced to growone or more of the MTJ material layers. For one or more of thesealternative deposition techniques, at least the magnetic material layersmay be deposited with at least some microstructure (e.g.,polycrystalline with texture).

At operation 640, a fixed magnetic material layer, or stack, comprisingCoFeB is deposited directly on the second Ta layer. At operation 645, atunneling dielectric material, such as MgO, is deposited over the fixedmagnetic layer. At operation 650 a free magnetic material layer or stackcomprising CoFeB is deposited over the tunneling dielectric material. Atoperation 655, a dielectric cap material, such as MgO, is deposited overthe free magnetic material layer or stack. Deposition of dielectric capmaterial is optional, and may be omitted from the fabrication processfor a spin-hall effect implementation of pSTTM, for example. Atoperation 660, a second electrode metal is deposited over the capmaterial. In exemplary embodiments, operations 640, 645, 650, 655, and660 all entail a physical vapor deposition (sputter deposition)performed at a temperature below 250° C. One or more of co-sputteringand reactive sputtering may be utilized in any capacity known in the artto form the various layer compositions described herein. For PVDembodiments, one or more of the material layers, such as but not limitedto the magnetic fixed and free material layers, are deposited inamorphous form that may be discontinuous over a substrate area (e.g.,forming islands that do not coalesce). Alternate deposition techniques,such as atomic layer deposition (ALD) may be performed for thosematerials having precursors known to be suitable. Alternatively,epitaxial processes such as, but not limited to, molecular beam epitaxy(MBE) may be practiced to grow one or more of the MTJ material layers.For one or more of these alternative deposition techniques, at least themagnetic material layers may be deposited with at least somemicrostructure (e.g., polycrystalline with texture).

After one or more layers of the MTJ material stack (e.g., all layers)are deposited, an anneal is performed under any conditions known in theart, for example to promote solid phase epitaxy of amorphous CoFeBmagnetic material layers imparting polycrystalline BCC structure and(001) texture. Anneal temperatures, durations, and environments may varywith exemplary embodiments performing an anneal at 250° C., or more.Method 601 is completed at operation 690 where high temperature STTMand/or MOS transistor IC processing is performed, for example at atemperature of at least 400° C. Any standard microelectronic fabricationprocesses such as lithography, etch, thin film deposition, planarization(e.g., CMP), and the like may be performed to complete delineationand/or interconnection of an STTM device employing any of the MTJmaterial stacks described herein or a subset of the material layerstherein.

In an embodiment, the MTJ functions essentially as a resistor, where theresistance of an electrical path through the MTJ may exist in tworesistive states, either “high” or “low,” depending on the direction ororientation of magnetization in the free magnetic layer(s) and in thefixed magnetic layer(s). In the case that the spin direction is down(minority) in the free magnetic layer(s), a high resistive state existsand the directions of magnetization in the coupled free magneticlayer(s) and the fixed magnetic layer(s) are anti-parallel with oneanother. In the case that the spin direction is up (majority) in thefree magnetic layer(s), a low resistive state exists, and the directionsof magnetization in the free magnetic layer(s) and the fixed magneticlayer(s) are parallel with one another. The terms “low” and “high” withregard to the resistive state of the MTJ are relative to one another. Inother words, the high resistive state is merely a detectibly higherresistance than the low resistive state, and vice versa. Thus, with adetectible difference in resistance, the low and high resistive statescan represent different bits of information (i.e. a “0” or a “1”).

The direction of magnetization in the coupled free magnetic layers maybe switched through a process called spin transfer torque (“STT”) usinga spin-polarized current. An electrical current is generallynon-polarized (e.g. consisting of about 50% spin-up and about 50%spin-down electrons). A spin-polarized current is one with a greaternumber of electrons of either spin-up or spin-down. Passing a currentthrough the fixed magnetic layer may generate the spin-polarizedcurrent. The electrons of the spin polarized current from the fixedmagnetic layer tunnel through the tunneling barrier or dielectric layerand transfers its spin angular momentum to the free magnetic layer,wherein the free magnetic layer will orient its magnetic direction fromanti-parallel to that of the fixed magnetic layer or parallel. Thespin-hall effect may also be employed to generate spin-polarized currentthrough a particular electrode material that is in contact with a freemagnetic material layer. For such embodiments, the free magnetic layermay be oriented without applying current through the fixed magneticlayer and other material layers of the MTJ. In either implementation,the free magnetic layer may be returned to its original orientation byreversing the current. Thus, the MTJ may store a single bit ofinformation (“0” or “1”) by its state of magnetization. The informationstored in the MTJ is sensed by driving a current through the MTJ. Thefree magnetic layer(s) does not require power to retain its magneticorientations. As such, the state of the MTJ is preserved when power tothe device is removed. Therefore, a spin transfer torque memory bit cellcomposed of the material stacks described herein is non-volatile.

FIG. 7 is a schematic of a STTM bit cell 701, which includes a spintransfer torque element 710, in accordance with an embodiment of thepresent invention. The spin transfer torque element 710 includes a freemagnetic material layer or stack 140 including at least one layer ofmagnetic material, such as CoFeB. Element 710 further includes firstmetallization 107 proximate to fixed magnetic layer 120 with anelectrode interface material 110 and seed layer 116 disposed therebetween. Tunneling layer 130 is disposed between free magnetic materiallayer/stack 140 and fixed magnetic layer/stack 120. A secondmetallization 180 is proximate to free magnetic material. Secondmetallization 180 is electrically coupled to a first metal interconnect792 (e.g., bit line). First metallization 107 is electrically connectedto a second metal interconnect 791 (e.g., source line) through atransistor 715. The transistor 715 is further connected to a third metalinterconnect 793 (e.g., word line) in any manner conventional in theart. In SHE implementations, second metallization 180 is further coupledto a fourth metal interconnect 794 (e.g., maintained at a referencepotential relative to first metal interconnect 792). The spin transfertorque memory bit cell 701 may further include additional read and writecircuitry (not shown), a sense amplifier (not shown), a bit linereference (not shown), and the like, as understood by those skilled inthe art of solid state non-volatile memory devices. A plurality of thespin transfer torque memory bit cell 710 may be operably connected toone another to form a memory array (not shown), wherein the memory arraycan be incorporated into a non-volatile memory device.

FIG. 8 illustrates a system 800 in which a mobile computing platform 805and/or a data server machine 806 employs MTJ material stacks comprisinga bottom electrode interface material layer or stack, for exampleincluding CoFeB or Ta as described above. The server machine 806 may beany commercial server, for example including any number ofhigh-performance computing platforms disposed within a rack andnetworked together for electronic data processing, which in theexemplary embodiment includes a packaged device 850.

The mobile computing platform 805 may be any portable device configuredfor each of electronic data display, electronic data processing,wireless electronic data transmission, or the like. For example, themobile computing platform 805 may be any of a tablet, a smart phone,laptop computer, etc., and may include a display screen (e.g., acapacitive, inductive, resistive, or optical touchscreen), a chip-levelor package-level integrated system 810, and a battery 815.

Whether disposed within the integrated system 810 illustrated in theexpanded view 820, or as a stand-alone packaged device within the servermachine 806, SOC 860 includes MTJ material stacks including bottomelectrode interface material layer or stack, for example including CoFeBor Ta. SOC 560 may further include a memory circuitry and/or a processorcircuitry 840 (e.g., STTM, MRAM, a microprocessor, a multi-coremicroprocessor, graphics processor, etc.). Any of controller 835, PMIC830, or RF (radio frequency) integrated circuitry (RFIC) 825 may includeembedded STTM employing MTJ material stacks including a NM/FM/NMmulti-layer filter stack, for example having at least one Ta-basedmaterial.

As further illustrated, in the exemplary embodiment, RFIC 825 has anoutput coupled to an antenna (not shown) to implement any of a number ofwireless standards or protocols, including but not limited to Wi-Fi(IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long termevolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA,TDMA, DECT, Bluetooth, derivatives thereof, as well as any otherwireless protocols that are designated as 3G, 4G, 5G, and beyond. Inalternative implementations, each of these SoC modules may be integratedonto separate ICs coupled to a package substrate, interposer, or board.

FIG. 9 is a functional block diagram of a computing device 900, arrangedin accordance with at least some implementations of the presentdisclosure. Computing device 900 may be found inside platform 905 orserver machine 906, for example. Device 900 further includes amotherboard 902 hosting a number of components, such as, but not limitedto, a processor 904 (e.g., an applications processor), which may furtherincorporate embedded magnetic memory based on MTJ material stackscomprising a bottom electrode interface material layer or stack, forexample including CoFeB or Ta as described above, in accordance withembodiments of the present invention. Processor 904 may be physicallyand/or electrically coupled to motherboard 902. In some examples,processor 904 includes an integrated circuit die packaged within theprocessor 904. In general, the term “processor” or “microprocessor” mayrefer to any device or portion of a device that processes electronicdata from registers and/or memory to transform that electronic data intoother electronic data that may be further stored in registers and/ormemory.

In various examples, one or more communication chips 906 may also bephysically and/or electrically coupled to the motherboard 902. Infurther implementations, communication chips 906 may be part ofprocessor 904. Depending on its applications, computing device 900 mayinclude other components that may or may not be physically andelectrically coupled to motherboard 902. These other components include,but are not limited to, volatile memory (e.g., DRAM), non-volatilememory (e.g., ROM), flash memory, a graphics processor, a digital signalprocessor, a crypto processor, a chipset, an antenna, touchscreendisplay, touchscreen controller, battery, audio codec, video codec,power amplifier, global positioning system (GPS) device, compass,accelerometer, gyroscope, speaker, camera, and mass storage device (suchas hard disk drive, solid-state drive (SSD), compact disk (CD), digitalversatile disk (DVD), and so forth), or the like.

Communication chips 906 may enable wireless communications for thetransfer of data to and from the computing device 900. The term“wireless” and its derivatives may be used to describe circuits,devices, systems, methods, techniques, communications channels, etc.,that may communicate data through the use of modulated electromagneticradiation through a non-solid medium. The term does not imply that theassociated devices do not contain any wires, although in someembodiments they might not. Communication chips 906 may implement any ofa number of wireless standards or protocols, including but not limitedto those described elsewhere herein. As discussed, computing device 900may include a plurality of communication chips 906. For example, a firstcommunication chip may be dedicated to shorter-range wirelesscommunications, such as Wi-Fi and Bluetooth, and a second communicationchip may be dedicated to longer-range wireless communications such asGPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

While certain features set forth herein have been described withreference to various implementations, this description is not intendedto be construed in a limiting sense. Hence, various modifications of theimplementations described herein, as well as other implementations,which are apparent to persons skilled in the art to which the presentdisclosure pertains are deemed to lie within the spirit and scope of thepresent disclosure.

It will be recognized that the invention is not limited to theembodiments so described, but can be practiced with modification andalteration without departing from the scope of the appended claims. Forexample the above embodiments may include specific combinations offeatures as further provided below.

In one or more first embodiments, a magnetic tunneling junction (MTJ)material layer stack disposed over a substrate includes anantiferromagnetic layer or stack, a multi-layered filter stack furthercomprising a first magnetic material layer disposed between twonon-magnetic material layers. At least one of the non-magnetic materiallayers comprises at least one of Ta, Mo, Nb, or Hf. The MTJ stackfurther including a fixed magnetic material layer or stack comprisingone or more second layers of magnetic material disposed between thefilter stack and a free magnetic material layer or stack comprising oneor more third layers of magnetic material. The MTJ stack furtherincluding a first layer of dielectric material disposed between thefixed magnetic material layer or stack, and the free magnetic materiallayer or stack.

In furtherance of the first embodiments, the magnetic material layershave perpendicular magnetic anisotropy. The antiferromagnetic layer orstack comprises a synthetic antiferromagnet (SAF) stack. A first of thenon-magnetic material layers in the filter stack is in direct contactwith the first magnetic material layer and a material layer of the SAFstack. A second of the non-magnetic material layers in the filter stackis in direct contact with the first magnetic material layer and one ofthe second layers of magnetic material.

In furtherance of the first embodiments immediately above, both of thenon-magnetic material layers in the filter stack comprise Ta and eachhas a film thickness between 0.1 nm and 0.5 nm.

In furtherance of the first embodiments immediately above, the second ofthe non-magnetic material layers in the filter stack has a greater filmthickness than does the first of the non-magnetic material layers.

In furtherance of the first embodiments, each of the non-magneticmaterial layers in the filter stack is at least predominantly Ta and hasa film thickness of 0.2 nm-0.5 nm.

In furtherance of the first embodiments, each of the non-magneticmaterial layers in the filter stack consists of Ta.

In furtherance of the first embodiments, both of the non-magneticmaterial layers in the filter stack comprise at least one of Ta, Mo, Nb,W, or Hf and each has a film thickness between 0.1 nm and 0.5 nm.

In furtherance of the first embodiments immediately above, both of thenon-magnetic material layers comprise Mo and each has a film thicknessbetween 0.1 nm and 0.5 nm.

In furtherance of the first embodiments, the first, second and thirdmagnetic material layers comprise CoFeB, the first dielectric materiallayer comprises MgO, and the first magnetic material layer has thicknessbetween 0.4 and 0.9 nm.

In one or more second embodiments, a non-volatile memory cell, comprisesa first electrode, a second electrode coupled to first interconnectmetallization of the memory array, the MTJ material stack in any of thefirst embodiments, and a transistor with a first terminal electricallycoupled to the first electrode, a second terminal electrically coupledto a second interconnect metallization of the memory array, and a thirdterminal electrically coupled to a third interconnect metallization ofthe memory array.

In one or more third embodiments, a non-volatile memory cell, comprisesa first electrode, a second electrode coupled to first interconnectmetallization of the memory array, and a MTJ material stack disposedbetween the first and second electrodes. The MTJ material stack furthercomprises an antiferromagnetic layer or stack, a multi-layered filterstack further comprising a first magnetic material layer disposedbetween two non-magnetic material layers, wherein at least one of thenon-magnetic material layers comprises at least one of Ta, Mo, Nb, orHf, a fixed magnetic material layer or stack comprising one or moresecond layers of magnetic material disposed between the filter stack anda free magnetic material layer or stack comprising one or more thirdlayers of magnetic material, and a first layer of dielectric materialdisposed between the fixed magnetic material layer or stack, and thefree magnetic material layer or stack. The MTJ stack further comprises atransistor with a first terminal electrically coupled to the firstelectrode, a second terminal electrically coupled to a secondinterconnect metallization of the memory array, and a third terminalelectrically coupled to a third interconnect metallization of the memoryarray.

In furtherance of the third embodiments, the magnetic material layershave perpendicular magnetic anisotropy, the antiferromagnetic layer orstack comprises a synthetic antiferromagnet (SAF) stack, the magneticmaterial layers each comprise Fe-rich CoFeB, the first dielectric layercomprises MgO, each of a first and a second non-magnetic material layerin the filter stack has thickness between 0.1 and 0.5 nm, and at leastone of the non-magnetic layers in the filter stack comprises atransition metal selected from the group consisting of: Ta, Mo, Nb, W,and Hf.

In furtherance of the third embodiments immediately above, the firstmagnetic material layer has thickness between 0.4 and 0.9 nm, and eachof the non-magnetic material layers in the filter stack consists of Taand has a film thickness of 0.2 nm-0.5 nm.

In furtherance of the third embodiments immediately above, the second ofthe non-magnetic material layers in the filter stack has a greater filmthickness than does the first of the non-magnetic material layers.

In one or more fourth embodiment, a mobile computing platform comprisesa non-volatile memory comprising a plurality of the non-volatile memorycell in any one of the third embodiments, a processor communicativelycoupled to the non-volatile memory, a battery coupled to the processor,and a wireless transceiver.

In one or more fifth embodiments, a method of forming a magnetictunneling junction (MTJ) material stack comprises depositing anantiferromagnetic layer or stack, depositing a first non-magnetic filterlayer over the antiferromagnetic layer or stack, depositing a firstmagnetic material layer over the first non-magnetic filter layer,depositing a second non-magnetic filter layer over the magnetic materiallayer, depositing a fixed magnetic material layer or stack comprisingone or more second layers of magnetic material over the secondnon-magnetic filter layer, depositing a dielectric material layer overthe fixed magnetic material layer or stack, depositing a free magneticmaterial layer or stack comprising one or more third layers of magneticmaterial over the dielectric material layer, and annealing the MTJ stackat a temperature of at least 250° C., wherein at least one of the firstor second non-magnetic filter layer comprises Ta, Mo, Nb, or Hf.

In furtherance of the fifth embodiments, depositing the firstnon-magnetic filter layer further comprises sputter depositing Ta to athickness of 0.2 nm-0.5 nm. Depositing the second non-magnetic filterlayer further comprises sputter depositing Ta to a thickness of 0.2nm-0.5 nm.

In furtherance of the fifth embodiments immediately above, depositingthe first magnetic material layer further comprises sputter depositingCoFeB directly on the first non-magnetic filter layer. Depositing thesecond non-magnetic filter layer further comprises sputter depositingthe Ta directly on the CoFeB. Depositing the fixed magnetic materiallayer or stack further comprises sputter depositing CoFeB directly onthe second non-magnetic filter layer.

In furtherance of the fifth embodiments, depositing the first, secondand third magnetic material layers comprises sputter depositingamorphous CoFeB, and the annealing converts the amorphous CoFeB intopolycrystalline BCC CoFeB with (001) texture.

In furtherance of the fifth embodiments, depositing the MTJ stackfurther comprises sputter depositing all of the layers at a temperaturebelow 250° C.

In furtherance of the fifth embodiments, depositing theantiferromagnetic layer or stack further comprises depositing a firstplurality of Co/Pt bi-layers, a Ru material layer over the firstplurality of Co/Pt bi-layers, and a second plurality of Co/Pt bi-layersover the Ru material layer.

However, the above embodiments are not limited in this regard and, invarious implementations, the above embodiments may include theundertaking only a subset of such features, undertaking a differentorder of such features, undertaking a different combination of suchfeatures, and/or undertaking additional features than those featuresexplicitly listed. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1-20. (canceled)
 21. A magnetic tunneling junction (MTJ) material layerstack over a substrate, the stack comprising: an antiferromagneticlayer; a multi-layered filter stack further comprising a first magneticmaterial layer between two non-magnetic material layers, wherein atleast one of the non-magnetic material layers comprises at least one ofTa, Mo, Nb, or Hf; a fixed magnetic material layer comprising one ormore second layers of magnetic material and between the filter stack anda free magnetic material layer comprising one or more third layers ofmagnetic material; and a first layer of dielectric material between thefixed magnetic material layer and the free magnetic material layer. 22.The material stack of claim 1, wherein: the magnetic material layershave perpendicular magnetic anisotropy; the antiferromagnetic layer isone material layer of a synthetic antiferromagnet (SAF) stack; a firstof the non-magnetic material layers in the filter stack is in directcontact with the first magnetic material layer and with a material layerof the SAF stack; a second of the non-magnetic material layers in thefilter stack is in direct contact with the first magnetic material layerand with one of the second layers of magnetic material.
 23. The materialstack of claim 22, wherein both of the non-magnetic material layers inthe filter stack comprise Ta and each has a film thickness between 0.1nm and 0.5 nm.
 24. The material stack of claim 23, wherein the second ofthe non-magnetic material layers in the filter stack has a greater filmthickness than the first of the non-magnetic material layers.
 25. Thematerial stack of claim 23, wherein each of the non-magnetic materiallayers in the filter stack is predominantly Ta and has a film thicknessof 0.2 nm-0.5 nm.
 26. The material stack of claim 25, wherein each ofthe non-magnetic material layers in the filter stack comprisessubstantially pure Ta.
 27. The material stack of claim 22, wherein bothof the non-magnetic material layers in the filter stack comprise atleast one of Ta, Mo, Nb, W, or Hf and each has a film thickness between0.1 nm and 0.5 nm.
 28. The material stack of claim 27, wherein both ofthe non-magnetic material layers comprise Mo and each has a filmthickness between 0.1 nm and 0.5 nm.
 29. The material stack of claim 21,wherein: the first, second and third magnetic material layers compriseCoFeB; the first dielectric material layer comprises an oxide of Mg; andthe first magnetic material layer has thickness between 0.4 and 0.9 nm.30. A non-volatile memory device, comprising: a first electrode; asecond electrode coupled to first interconnect metallization of thememory array; a MTJ material stack between the first and secondelectrodes, wherein the MTJ material stack further comprises: anantiferromagnetic layer; a multi-layered filter stack further comprisinga first magnetic material layer between two non-magnetic materiallayers, wherein at least one of the non-magnetic material layerscomprises at least one of Ta, Mo, Nb, or Hf; a fixed magnetic materiallayer or stack comprising one or more second layers of magnetic materialbetween the filter stack and a free magnetic material layer comprisingone or more third layers of magnetic material; and a first layer ofdielectric material between the fixed magnetic material layer and thefree magnetic material layer; and a transistor with a first terminalelectrically coupled to the first electrode, a second terminalelectrically coupled to a second interconnect metallization of thememory array, and a third terminal electrically coupled to a thirdinterconnect metallization of the memory array.
 31. The memory device ofclaim 30, wherein: the magnetic material layers have perpendicularmagnetic anisotropy; the antiferromagnetic layer is one material layerof a synthetic antiferromagnet (SAF) stack; the magnetic material layerseach comprise Fe-rich CoFeB; the first dielectric layer comprises anoxide of Mg; each of a first and a second non-magnetic material layer inthe filter stack has thickness between 0.1 and 0.5 nm; and at least oneof the non-magnetic layers in the filter stack comprises at least one ofTa, Mo, Nb, W, or Hf.
 32. The memory device of claim 31, wherein: thefirst magnetic material layer has thickness between 0.4 and 0.9 nm; andeach of the non-magnetic material layers in the filter stack consists ofTa and has a film thickness of 0.2 nm-0.5 nm.
 33. The memory device ofclaim 32, wherein the second of the non-magnetic material layers in thefilter stack has a greater film thickness than does the first of thenon-magnetic material layers.
 34. A mobile computing platformcomprising: a non-volatile memory comprising a plurality of thenon-volatile memory cell of claim 30; a processor communicativelycoupled to the non-volatile memory; a battery coupled to the processor;and a wireless transceiver.
 35. A method of forming a magnetic tunnelingjunction (MTJ) material stack, comprising: depositing anantiferromagnetic layer or stack; depositing a first non-magnetic filterlayer over the antiferromagnetic layer or stack; depositing a firstmagnetic material layer over the first non-magnetic filter layer;depositing a second non-magnetic filter layer over the magnetic materiallayer; depositing a fixed magnetic material layer comprising one or moresecond layers of magnetic material over the second non-magnetic filterlayer; depositing a dielectric material layer over the fixed magneticmaterial layer; depositing a free magnetic material layer over thedielectric material layer; and annealing the MTJ stack at a temperatureof at least 250° C., wherein at least one of the first or secondnon-magnetic filter layer comprises at least on of Ta, Mo, Nb, or Hf.36. The method of claim 35, wherein: depositing the first non-magneticfilter layer further comprises sputter depositing Ta to a thickness of0.2 nm-0.5 nm; and depositing the second non-magnetic filter layerfurther comprises sputter depositing Ta to a thickness of 0.2 nm-0.5 nm.37. The method of claim 36, wherein: depositing the first magneticmaterial layer further comprises sputter depositing CoFeB directly onthe first non-magnetic filter layer; depositing the second non-magneticfilter layer further comprises sputter depositing the Ta directly on theCoFeB; and depositing the fixed magnetic material layer or stack furthercomprises sputter depositing CoFeB directly on the second non-magneticfilter layer.
 38. The method of claim 35, wherein: depositing the first,second and third magnetic material layers comprises sputter depositingamorphous CoFeB; and the annealing converts the amorphous CoFeB intopolycrystalline BCC CoFeB with (001) texture.
 39. The method of claim34, wherein depositing the MTJ stack further comprises sputterdepositing all of the layers at a temperature below 250° C.
 40. Themethod of claim 34, wherein depositing the antiferromagnetic layerfurther comprises depositing a first plurality of Co/Pt bi-layers, a Rumaterial layer over the first plurality of Co/Pt bi-layers, and a secondplurality of Co/Pt bi-layers over the Ru material layer.